A titanium alloy has such a small specific gravity and remarkable corrosion resistance that it is used for blades at the last stage or low-temperature stages of a low-pressure turbine among steam turbines, and for blades at preceding and low-temperature stages of a compressor in gas turbines or aircraft engines. Under the above application circumstances, the low-pressure turbine among the steam turbines is exposed to a high-speed collision of wet steam, causing erosion (water droplet erosion) and abrasion of the turbine blades due to the water droplets contained therein. And, suction of a large volume of air by the compressor in the gas turbines and the aircraft engines causes sand or dust included in the air to hit the turbine blades to wear away or erode (sand erosion) the turbine blades.
Damages due to the erosion will be described with reference to FIG. 1, FIG. 2 and FIG. 3. FIG. 1 is a perspective view showing one example of the shape of turbine blades for a steam turbine, and FIG. 2 is a perspective view showing one example of the shape of turbine blades for an aircraft engine, and FIG. 3 is a presentative view showing one example of turbine blades having cover and snubber. FIG. 1 to FIG. 3 show that erosion is caused concentrated on the leading edges rotating at a high speed on the tip portions when blades 1 rotate. Eroded portions 2 are indicated by mark X. Reference numeral 3, 4a, and 4b indicate a turbine rotor, covers, and snubber portion, respectively.
Conventional methods to prevent such erosion include to weld or braze a hard material such as a Co-based alloy, such as stellite (trademark of Cabot Corp), or a Ti-15Mo-5Zr-3Al alloy excellent in erosion resistance to the leading edges on the tip portions of the blades which tend to be eroded, or coat them with ceramics or the like.
But, the junction or coating of the above special materials has disadvantages that the welded or brazed section or the coating interface includes the connection of different materials and heat affected zones, causing a high residual stress and an embrittlement phase, as well as a large distortion, so that strength is lowered and a long-term reliability is inferior.
To remedy the above disadvantages, the present invention has been completed and aims to provide a method for producing titanium alloy turbine blades which can be produced economically, can prevent erosion from occurring, and is superior in reliability.
The present invention further aims to provide titanium alloy turbine blades excellent in erosion resistance at the leading edges of the tip portions of the blades including covers and in reliability.